Contact lenses are widely used for many different types of vision deficiencies. These include defects such as near-sightedness and far-sightedness (myopia and hypermetropia, respectively), and defects in near range vision usually associated with aging (presbyopia). Presbyopia occurs as a person ages when the lens of eye begins lose its elasticity, eventually resulting in the eye losing the ability to focus on near objects. Such an individual will require additional vision correction for reading or working with a computer.
Some presbyopic persons have both near vision and far vision defects, requiring bifocal or multifocal lenses to properly correct their vision.
A typical single vision contact lens has a real or virtual focus, which is the point on which parallel rays of light focus when the lens is placed perpendicular to the parallel rays, and an optical axis, which is an imaginary line drawn from the focus to the center of the lens. The lens has a posterior surface that fits against the cornea and an opposite anterior surface. The optical zone, or zones, of the lens focus light to correct the eye's vision. In the case of a typical spherical lens, the optical zone has a single radius of curvature that is the distance from any point on the vision surface to a point on the optical axis referred to as the center of curvature.
A bifocal contact lens has at least two optical zones: a distance zone, for distance vision correction, and a near optical zone, for near vision correction (e.g., while reading).
While bifocal contact lens allow a person to improve their distance vision and near vision, the bifocal contact lens compromises intermediate vision correction, such as viewing a computer screen. The bifocal contact lens does not provide the needed correction.
Therefore, there is a need for a bifocal or multifocal wear modality that provides support not only to distance and near vision correction, but also intermediate vision correction.